Conventionally, for Long Term Evolution (LTE) and LTE-Advanced as a next-generation mobile communication system, a heterogeneous network has been studied aiming at enlarging system capacity and coverage. The heterogeneous network is a network in which a macrocell and a cell constituted by a base station with low transmission power (hereinafter referred to as a “picocell”) are arranged in a coexisting manner. In such a network, when the macrocell and the picocell are operated at the same frequency, interference from the macrocell to a picocell becomes a problem. In other words, in a mobile station (hereinafter referred to as a “pico base station”) connected to a base station of the picocell (hereinafter referred to as a “pico mobile station”), a signal from the pico base station is interfered with by a signal from a base station of the macrocell (hereinafter referred to as a “macro base station”).
The above-described inter-cell interference influences the communication quality in physical channels (a control channel and a shared channel). In particular, in a system in which subframe transmission timing is synchronized between cells, the inter-cell interference may occur between the control channels and between the shared channels. As a technology that reduces the inter-cell interference, an inter-cell coordination control technology can be adopted. Examples of the inter-cell coordination control technologies can include a technology called Coordinated Multiple Point (CoMP), which is under study in LTE-Advanced (Release-11), and another technology called Inter-Cell Interference Coordination (ICIC) in LTE (Release-8). In the inter-cell coordination control technologies such as CoMP and ICIC, a plurality of base stations are coordinated to transmit a data signal using the shared channel to a mobile station.
In recent LTE, there is concern about a shortage of the capacity of the control channel when communications are performed simultaneously among many users. As a technology for solving the capacity shortage of the control channel, a technology is under study that enhances the control channel to a shared channel region or the like. This technology frequency-multiplexes a Physical Downlink Control Channel (PDCCH) as one of the control channels to resources of a Physical Downlink Shared Channel (PDSCH) as a shared channel, thereby enhancing the PDCCH. The enhanced PDCCH is called Enhanced-PDCCH (E-PDCCH)
Non Patent Literature 1: 3GPP TS 36.211 V10.2.0 (2011-06)
Non Patent Literature 2: 3GPP TS 36.212 V10.2.0 (2011-06)
Non Patent Literature 3: 3GPP TS 36.213 V10.2.0 (2011-06)
Non Patent Literature 4: 3GPP TR 36.814 V9.0.0 (2010-03)
Non Patent Literature 5: 3GPP R1-111636 (2011-05)
The conventional technology does not consider reducing the inter-cell interference of the control channel enhanced to the shared channel region or the like.
For example, in the E-PDCCH, which is the control channel enhanced to the shared channel region or the like, inter cell coordination control such as CoMP and ICIC is considered to be adopted as is the case with the PDSCH as the shared channel. However, it is difficult for the E-PDCCH that is currently under study to adopt the inter-cell coordination control such as CoMP and ICIC, because of being arranged in a scattered manner across the entire bandwidth allocated. As a result, control signals using the E-PDCCH may interfere with each other between cells.